The present invention relates to a method for selecting a semiconductor integrated optical modulator/laser light source device comprising a modulator section and a laser section.
A semiconductor optical modulator integrated laser light source device having a laser device, such as a distributed feed back laser or a distributed reflection laser, and a modulator, such as an electroabsorption modulator, is increasingly popular because this light source device shows a small chirping when the modulator shows a modulation. The property of the small chirping of the laser device is suitable for a long-distance and large capacitance optical signal transmission. In the semiconductor optical modulator integrated laser light source device, the laser section is driven by a direct current and the modulator section is driven by pulse signals having binary levels wherein when one level is -applied onto the modulator section, the modulator performs an attenuation function thereby the laser beam is absorbed in the modulator, resulting in almost no laser emission being obtained. By contrast, another level is applied onto the modulator section, the modulator shows no attenuation function thereby the laser beam pass through in the modulator without any attenuation, resulting in a laser emission being obtained.
This semiconductor optical modulator integrated laser light source device, however, has problems generating a bit error due to the following reasons.
A first reason for generation of the bit error associated with the semiconductor optical modulator integrated laser light source device is concerned with a generation of wavelength chirping which is caused by optical and electrical interference between the laser section and the modulator section in the semiconductor optical modulator integrated laser light source device. The optical and electrical interference between the laser section and the modulator section may often be generated when an isolation resistance between the laser section and the modulator section is small or when the modulator section has a facet showing an insufficient reflective suppression function.
A second reason for generation of the bit error associated with the semiconductor optical modulator integrated laser light source device is concerned with a variation in optical power due to an influence of an electrical multiplication reflection which is caused by an impedance mismatching between the modulator and a modulator driver circuit for driving the modulator.
A third reason for generation of the bit error associated with the semiconductor optical modulator integrated laser light source device is concerned with an increase of the wavelength chirping of the modulator section due to increasing phase modulation caused by a carrier accumulation. The carrier accumulated is generated by an optical absorption into the modulator section.
Therefore, it is required to verify whether the semiconductor optical modulator integrated laser light source device is available to be free from the above described problem with the bit error. In the prior art, the verifying process is accomplished by making a complicated measurement of a property of the transmission bit error rate associated with the semiconductor integrated optical modulator/laser light source device wherein the measurement of the transmission bit error rate property requires conducting an optical signal transmission test under the same conditions as the practical use and further confirming whether or not there exists a bit error for each of an extremely large numbers of bits as signals having transmitted in the test. Thus, it has been required to develop a quite novel method for selection thereof free from the above problem.